In a first aspect, this invention relates to a liquid-damming protective bank of the kind which comprises a member, e.g. a flexible, liquid-filled casing and/or a flexible skirt, abutting against a surface, e.g. the ground, upon which a vertical force acts with the purpose of pressing and anchoring the same against the surface, said protective bank having a first long side edge turned towards a flood side and an opposite, second long side edge turned towards a dry side of the bank.
Phenomena of flood may occur in very different areas and under very different circumstances. A frequent type of flood may hit houses situated in the vicinity of watercourses, e.g. lakes and rivers, temporarily overflowing their banks due to extreme precipitation. Water may then flow by surface over the ground to the house and cause various damage thereto, such as filling possible basement spaces with water or partial filling of localities on the ground floor. Water damage of this type are without exception very costly to master. In other cases, fluids of another type than water, e.g. oil, fuels, chemicals and the like, may spill over on areas or surfaces as a consequence of a leakage of an unexpected type.
Regardless of the type of the flood, there is a general ambition to try to countercheck the flood and to confine the proportions thereof, more precisely by erecting some type of protective bank which stems the liquid flow. The house-owner erects a bank surrounding the house with the purpose of preventing the water from approaching the same. Inversely, in case of a leakage, the protective bank is erected with the purpose of preventing the liquid from distancing from the source of leakage.
Conventional methods for erecting protective banks make use of solid materials, usually of a mineral nature. A common way is to manually lay out sandbags in more or less high rows. Another way is to erect banks of soil by means of suitable machines. However, these methods have disadvantages. To the extent that mechanical dredging or excavation is possible at all, the method is time-wasting and most often only possible to resort to at a late stage. Furthermore, it rather often causes pits and other wounds in the ground. The sandbag method is not only time-wasting but also laborious. Many times, neither machines nor sandbags are available in the immediate surroundings of the flood, and therefore time-consuming transportations have to be carried out before the erection of the bank can be started. This means that the protective bank may be in place too late.
With the purpose of obviating the disadvantages associated with earth banks and protective banks of sandbags respectively, it has lately been developed protective banks erected of mobile damming devices in the form of hose-like casings which may be stored, handled and transported in a collapsed state and filled with liquid, usually water, at the very site of a flood. Examples of such hose-casings are disclosed in abundance in the literature of patents. See, e.g. FR 1 375 854, EP 496 519, U.S. Pat. No. 3,246,474 , U.S. Pat. No. 3,855,800 , U.S. Pat. No. 4,799,821 and U.S. Pat. No. 5,040,919. A substantial advantage of such hose-casings is that they are diminutive in a collapsed state, at the same time as the weighty material which is required for anchoring the casings in a protective bank, usually is available in abundance at the site of the flood in the form of water. Well-nigh unlimited amounts of damming devices in the form of hose-casings may therefore quickly and smoothly be brought to a place hit by a flood and activated on site by the simple measure of filling the same with water. The majority of the previously known damming devices in the form of hose-casings also comprise a skirt turned towards the flood side, of more or less explicit width, most commonly being anchored by means of nail- or stud-like anchoring members, the purpose of which is to seal against the surface.
Another mobile damming device, commercially available under the trade mark of PORTADAM, makes use of an impermeable, skirt-like membrane abutting with a long side portion along the surface, having an opposite long side portion abutted against a framework erected in the line of defence and consisting of a plurality of oblique support legs.
One thing that the previously known protective banks using mobile or portable damming devices have in common, is that the member of the protective bank abutting against the surface is brought to abut against the same over its entire area in the praiseworthy purpose of obtaining the biggest possible tightness against the surface. Thus, the previously known constructions originate from the fundamental idea that the larger the area of contact against the surface, the more reliable becomes the protective bank. However, this fundamental idea is partly based on erroneous premises. Namely, if water, as often is the case in practice, after all starts to leak in under e.g. a skirt kept pressed against the surface by the hydraulic pressure acting on the top side of the skirt, the pressure difference between the top side and the bottom side of the skirt will be substantially reduced. This means that the area of the skirt influenced from below by the same hydraulic pressure as the top side, will lose its anchoring ability. If seepage water under hydraulic pressure is spread out under the skirt and/or the hose-casing all the way from the flood side to the dry side, the protective bank will gradually lose its anchoring ability and thereby its sealing ability against the surface, and finally be loosened from its line of defence. The same reduction of pressure difference exists, of course, also in those cases when a hose-casing without a skirt (see e.g. EP 496 519) is used to erect the protective bank. As soon as water starts to leak in under the surface of the hose-casing abutting against the ground, the total anchoring ability is gradually reduced, meaning that, in a state when the horizontal displacement force from the flood water exceeds the anchoring force, the casing simply floats away on the water lying under the same.
In this context, it should also be pointed out that flood water may find its way down in voids in the ground, under the surface thereof, and subsequently reappear on the surface and exert a lifting pressure against the bottom side of the protective bank.